build: limit plugin exports to official API symbols
TS-2635: remove unused include <net/ppp_defs.h>
TS-2423: Add option for server sessions that use auth headers that can
be placed into the shared pool
doc: update cluster docs for common issues
TS-2902: Allow POST requests without a Content-Length header
TS-2095: autoconf warnings related to unordered_map
Revert "TS-2095: autoconf warnings related to unordered_map"

This reverts commit 957e60b917bd80ce9ae1de3fdc7e47afaa8cfc08.
[TS-2947] Make the setting proxy.config.http.global_user_agent_header
overrideable.
Fix CHANGES indentation
TS-2902 Also add the new config to the regression tests
atscppapi: Added functionality to return request body in AsyncHttpFetch
atscppapi: Optimizing values() in Headers by removing size()/count() calls
atscppapi: fixing deadlock and shut down race conditions in intercept
TS-3004: Update vendor_name and support_email in ats_speed plugin
Update vendor_name and support_email in plugins
TS-2279: Update range for proxy.config.exec_thread.affinity
TS-2913 Missing body factory template for permanent redirects.
TS-2584: Remove assert for negatively cached transformed content.
TS-2982: Interim cache compile errors.
TS-2905: Fix IP logging to print '0' instead of error text.